1. Field of the Invention
The present invention relates to a digital video camera. More specifically, the present invention relates to a digital video camera in which a camera signal obtained from a CCD imager having a mosaic-type color filter or a stripe-type color filter is digitally processed such that an OB (optical black) level is clamped.
2. Description of the Prior Art
One example of a conventional digital video camera in which an OB level can be clamped with using a simple circuit is described in, for example, Japanese Patent Application Laying-open No. 5-244490 [H04N 5/243, 5/16, 5/335, 9/04, 9/72] laid-open on Sep. 21, 1993.
In the prior art, an offset is added to an output of a CCD imager, and a clamp level, which is calculated on the basis of an OB level at a back end of the output of the CCD imager, is subtracted from an addition result, and the offset is subtracted again from a subtraction result. Therefore, a video signal having no black level deviation can be obtained. In addition, "the black level deviation" means an phenomenon that a black level raised above a reference black level and thus a black imge is displayed as a grayish black image.
On the other hand, other examples of a digital video camera having a quadruplication mode are described in, for example, Japanese Patent Application Laying-open No. 63-250287 [H04N 5/225, 5/335, 3/00] laid-open on Oct. 18, 1988, Japanese Patent Application Laying-open No. 7-212657 [H04N 5/335, H01L 27/12] laid-open on Aug. 11, 1996, and a U.S. patent application Ser. No. 08/188,543 [H04N 5/335, H01L 27/12] filed on Jan. 28, 1994. In each of the prior art references only a portion of an output of a CCD imager is used as a camera signal, and the remainder is swept-out to a drain.
Accordingly, it is impossible to apply the former prior art to the latter prior art references because the output of the CCD imager having the OB level at the back end, the OB level being utilized in the former prior art, is swept-out in the latter prior art references.